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Abstract

This paper discusses the feasibility of coding an &quot;undetectable&quot; digital water mark on a standard 512*512 intensity image with an 8 bit gray scale. The watermark is capable of carrying such information as authentication or authorisation codes, or a legend essential for image interpretation. This capability is envisaged to fmd application in image tagging, copyright enforcement, counterfeit protection, and controlled access. Two methods of implementation are discussed. The first is based on bit plane manipulation of the LSB, which offers easy and rapid decoding. The second method utilises linear addition of the water mark to the image data, and is more difficult to decode, offering inherent security. This linearity property also allows some image processing, such as averaging, to take place on the image, without corrupting the water mark beyond recovery. Either method is potentially compatible with JPEG and MPEG processing. 1.

Citations

.... The autocorrelation function and spectral distribution of m-sequences resemble that of random Gaussian noise. The crosscorrelation of m-sequences has been examined mathematically and empirically in =-=[6]-=-. p] and [8]. Certain families of sequences (maximal connected sets) have been known to possess desirable crosscorrelation properties [9]. Images encoded with m-sequences or one bit Gaussian noise are...

...ability and accurate recovery of the hidden message. In general, the problem of embedding an invisible watermark and its subsequent extraction falls into the category of matched or adaptive filtering =-=[2]-=-. The authors have developed a simple modification of such a scheme. In order to render the watermark undetectable, encoding with msequences was chosen, because of their balance, random appearance and...

...detectable, encoding with msequences was chosen, because of their balance, random appearance and good autocorrelation properties (a single peak with no sidelobes), which simplify the recovery process =-=[3]-=-. In practice, extended m-sequences were employed, being commensurate with the image size (23 and exhibiting a null in autocorrelation around the main peak [4]. Two dimensional analogues such as Costa...

...mark due to cropping and distortions such as skew, rotations, translations etc, and countermeasures against these. These may include bit-swapping or diagonal raster folding of sequences into m-arrays =-=[12]-=-. These operations are facilitated by our choice of extended m-sequences of length 2”. The desirability of tamper-resistant watermarks could be a function of the application. Some implementations may ...

...es), which simplify the recovery process [3]. In practice, extended m-sequences were employed, being commensurate with the image size (23 and exhibiting a null in autocorrelation around the main peak =-=[4]-=-. Two dimensional analogues such as Costas Arrays were studied, but were rejected because of their sparse nature [SI. For simplicity. we have chosen to encode the water mark by the choice of msequence...

...rrelation function and spectral distribution of m-sequences resemble that of random Gaussian noise. The crosscorrelation of m-sequences has been examined mathematically and empirically in [6]. p] and =-=[8]-=-. Certain families of sequences (maximal connected sets) have been known to possess desirable crosscorrelation properties [9]. Images encoded with m-sequences or one bit Gaussian noise are statistical...

...-sequences has been examined mathematically and empirically in [6]. p] and [8]. Certain families of sequences (maximal connected sets) have been known to possess desirable crosscorrelation properties =-=[9]-=-. Images encoded with m-sequences or one bit Gaussian noise are statistically indistinguishable from each other and only visually distinguishable from the original if the image contains large areas wi...

...es varies according to the operations performed. Also, it is possible to utilise other sequences of the de Bruijn type, such as Legendre sequences, based on residues, and extremely difficult to crack =-=[ll]-=-. 3. MEI'HODS OF INCORPORATING THE WATER MARK Our experiments were conducted on 512*512 8 bit gray scale images encoded on a line by line basis with msequences z9 pixels long. The first method involve...